California Code of Civil Procedure Section 1013a

1013a. Proof of service by mail may be made by one of the following methods:

(1) An affidavit setting forth the exact title of the document served and filed in the cause, showing the name and residence or business address of the person making the service, showing that he or she is a resident of or employed in the county where the mailing occurs, that he or she is over the age of 18 years and not a party to the cause, and showing the date and place of deposit in the mail, the name and address of the person served as shown on the envelope, and also showing that the envelope was sealed and deposited in the mail with the postage thereon fully prepaid.

(2) A certificate setting forth the exact title of the document served and filed in the cause, showing the name and business address of the person making the service, showing that he or she is an active member of the State Bar of California and is not a party to the cause, and showing the date and place of deposit in the mail, the name and address of the person served as shown on the envelope, and also showing that the envelope was sealed and deposited in the mail with the postage thereon fully prepaid.

(3) An affidavit setting forth the exact title of the document served and filed in the cause, showing (A) the name and residence or business address of the person making the service, (B) that he or she is a resident of, or employed in, the county where the mailing occurs, (C) that he or she is over the age of 18 years and not a party to the cause, (D) that he or she is readily familiar with the business practice for collection and processing of correspondence for mailing with the United States Postal Service, (E) that the correspondence would be deposited with the United States Postal Service that same day in the ordinary course of business, (F) the name and address of the person served as shown on the envelope, and the date and place of business where the correspondence was placed for deposit in the United States Postal Service, and (G) that the envelope was sealed and placed for collection and mailing on that date following ordinary business practices. Service made pursuant to this paragraph, upon motion of a party served, shall be presumed invalid if the postal cancellation date or postage meter date on the envelope is more than one day after the date of deposit for mailing contained in the affidavit.

(4) In case of service by the clerk of a court of record, a certificate by that clerk setting forth the exact title of the document served and filed in the cause, showing the name of the clerk and the name of the court of which he or she is the clerk, and that he or she is not a party to the cause, and showing the date and place of deposit in the mail, the name and address of the person served as shown on the envelope, and also showing that the envelope was sealed and deposited in the mail with the postage thereon fully prepaid. This form of proof is sufficient for service of process in which the clerk or deputy clerk signing the certificate places the document for collection and mailing on the date shown thereon, so as to cause it to be mailed in an envelope so sealed and so addressed on that date following standard court practices. Service made pursuant to this paragraph, upon motion of a party served and a finding of good cause by the court, shall be deemed to have occurred on the date of postage cancellation or postage meter imprint as shown on the envelope if that date is more than one day after the date of deposit for mailing contained in the certificate.